In the field of manufacturing ophthalmic lenses, it is generally recognized in the prior art that the most economical means of forming such lenses is by molding a lens forming material between dies or molding members having smooth optical molding surfaces with the appropriate curvature to impart the desired optical properties. Generally the lens forming material is a polymer compound, such as an acrylic, methacrylate, polycarbonate, or the like.
It is evident that a critical factor in the molding of lenses is the molding members themselves. Generally, a large plurality of front surface and rear surface molds must be provided, each having a unique optical surface-forming characteristic. To fill a particular ophthalmic prescription, appropriate front surface and rear surface molding members are chosen, an optimal lens thickness is calculated for the two selected molds, and a gasket or the like is either selected or fabricated to secure the molds together to define the molding cavity. The cavity is then filled with lens compound, cured or polymerized by heat, radiation, or chemical action, and the finished lens is removed from the assembly.
The process outlined above requires a very large number of front and rear surface molds, in order to fill the hundreds of thousands of ophthalmic prescriptions commonly required. Furthermore, a large number of gaskets are required for this process, due to the fact that the gaskets must form a seal with the variously curved edge configurations of the mold members, and that the thickness of the lenses must be determined by the spacing of mold members created by the gaskets. In this regard, the mold spacing is generally measured between the confronting optical forming surfaces of the mold members. It is vital that the mold spacing be greater than a predetermined minimum, both to produce a lens of sufficient thickness and strength, and to prevent mold crashing and mutual destruction.
The large number of mold members and gaskets that must be inventoried to carry out the process described above represents a considerable capital investment which is difficult to recoup through commercial sales. Therefore it has been necessary in the prior art to simplify the process by reducing the number of components inventoried. The most straightforward simplification is to mold lenses having the desired front surface and a stock rear surface (or vice-versa) that can be ground to the desired finished lens by a dispensing optical laboratory or the like. This tactic introduces a post-manufacturing labor expense, and requires trained personnel for high quality lenses. Furthermore, it is not an improvement in the prior art molding technology, but rather an expedient shortcut to make the technology commercially viable. There is an obvious need in the prior art for a molding methodology that reduces the number of molding components while providing the capability of filling the large number of common ophthalmic prescriptions.